Dissolving complexes of anionic dye/cationic polymeric fixer

ABSTRACT

The invention relates to dissolving an anionic dye/cationic polymer complex including the step of applying to the complex a water-soluble solvent having a dielectric constant from 20 to 43 at standard temperature and pressure.

This is a division of application Ser. No. 10/354,624, filed Jan. 28,2003 now U.S. Pat. No. 6,998,429.

FIELD OF THE INVENTION

In inkjet printing, anionic dye and cationic polymer fixer are oftenused. Together they form a complex that sometimes must be dissolved andremoved from places where it has formed, such as the printhead.

BACKGROUND OF THE INVENTION

Dye-based inkjet inks have become a dominant technology in the inkjetink arena. However, as many dyes are water-soluble, images printed usingmany of such dye-based inkjet inks are not as waterfast as may bedesirable. The waterfastness and durability of anionic dye-based inkjetink printed on media has been shown to be enhanced by overprinting orunderprinting the printed image with a fixer, preferably from a separatepen. Fixers work to crash the colorants, e.g. anionic dyes, anionicpigments or carboxylated dyes, by changing the pH of the printed inkjetimage or by adding salts such as Ca²⁺ and Mg²⁺ to the printed inkjetimage. These fixers had the disadvantages of lacking durability, ofcausing pen wear and tear and corrosion due to the high salt content andthe low pH.

More recently, cationic polymers have been used in the fixer. Thus, whenthe cationic polymer and the anionic dye contact one another on asubstrate, a reaction between the dye and the polymer creates an imagewith improved durability and waterfastness. Inkjet images with improvedwaterfastness and durability can therefore be obtained by underprintingor overprinting a printed inkjet image with a cationic polymeric fixer.

Thus, anionic inks can be rendered more durable by printing with a fluidcontaining a cationic polymer. Sometimes during printing, the ink andthe polymer fluids come into contact on the surface of one of theprintheads, creating a durable complex which is difficult to remove withsuch servicing fluids as 1,2 hexanediol, glycerol and water.

SUMMARY OF THE INVENTION

The present invention relates to a method of dissolving an anionicdye/cationic polymer complex comprising the step of applying to thecomplex a water-soluble solvent having a dielectric constant from 20 to43 at standard temperature and pressure.

The present invention additionally relates to an inkjet printheadcleaning system, wherein an anionic dye/cationic polymer complex on theprinthead is removed by applying to the complex on the printhead awater-soluble solvent having a dielectric constant from 20 to 43 atstandard temperature and pressure.

Also, the present invention relates to a method of removing an anionicdye/cationic polymer complex from an inkjet printhead, comprising thestep of applying to the complex on the printhead a water-soluble solventhaving a dielectric constant from 20 to 43 at standard temperature andpressure.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of embodiments of the invention, referencewill now be made to the accompanying drawings in which:

FIGS. 1A and 1B plot the Fixer/Dye ratio against the % Colorant Solublefor complexes of anionic dyes with cationic fixers in deionized (DI)water.

FIGS. 2A and 2B plot the Fixer/Dye ratio against the % Colorant Solublefor complexes of anionic dyes with cationic fixers in 8% 2P.

FIGS. 3A and 3B plot the Fixer/Dye ratio against the % Colorant Solublefor complexes of anionic dyes with cationic fixers in 40% 2P.

FIGS. 4A and 4B plot the %2P against the % Colorant Soluble with theFixer/Dye Weight Ratio equal to 1/1.

DETAILED DESCRIPTION

In order to obtain images that are durable to highlighter smear or waterdrip and smudge, inks containing anionic dyes are underprinted and/oroverprinted with fluids containing cationic polymers. The dye/polymercomplex forms a durable mixture. When the ink and the polymer fluid endup on a printhead surface, the mixture is not easily removed by typicalwater-soluble servicing solvents such as 1,2-hexane diol, glycerol andwater.

Effective and Ineffective Water Soluble Solvents

To study which water-soluble servicing solvents are best for removingthe ink/polymer complex, the solubility of the precipitate formedbetween dye and fixers was evaluated in a variety of solvents.Specifically inks and fixers were pipetted onto cellulose TLC plates,dried and developed in a variety of solvents as described in Examples 1and 2.

As shown in the Examples below, it was found that the dye/fixer complexprecipitate is immobile in water, dipropylene glycol, 1,2 hexanediol,and 1,6-hexanediol indicating a lack of solubility in these solvents. In2-amino-2-methyl propanol and 1,2 propanediol, it was found that some,but not all, of the complex precipitates are mobile, indicating that atleast some of the complex precipitates are soluble in these solvents.

Also in the Examples, it is seen that all of the complex precipitatesare mobile and therefore solubilized in 2-pyrrolidone, diethyleneglycol, 1,2-propanediol, tetraethylene glycol, 1-methyl-2-pyrrolidoneand n,n-dimethyl propionamide.

It has been found that 2-pyrrolidone is very effective at dissolving thedye-polymer complex. Furthermore, mixtures of 2-pyrrolidone and waterare capable of dissolving the complex and are compatible with theprinthead materials. The weight percentage ratio of 2-pyrrolidone towater can be from 100:0 to 20:80. In a preferred embodiment, the weightpercentage ratio is 40:60.

It has also been found that 2-pyrrolidone inhibits precipitation of theanionic dye/cationic polymeric fixer complex as manifested by a greaterequilibrium solubility and a slower precipitation rate. No precipitationwas observed in systems containing more than 45 weight % 2-pyrrolidone.

Dielectric constants at standard temperature and pressure for most ofthe water-soluble servicing solvents tested have been obtained atstandard temperature and pressure. Generally, it has been found thatsolvents that are “effective” at solubilizing anionic dye/cationic fixercomplexes have dielectric constants that fall within the range of fromapproximately 20 to approximately 43 at standard temperature andpressure. In contrast, it has been found that solvents that are“ineffective” at solubilizing anionic dye/cationic fixer complexes havedielectric constants that fall outside the above range of 20-43 atstandard temperature and pressure. Comparative tables are shown below:

Dielectric Constants at STP “Effective” Solvents 2-pyrrolidone 28.18Diethylene glycol 31.82 1,2-propanediol 32 Tetraethylene glycol 20.441-methyl-2-pyrrolidone 32.2 N,n-dimethylpropionamide 34.6 Triethyleneglycol 23.7 1,5-pentanediol 26.2 1,4-pentanediol 31.9 “Ineffective”Solvents Water 78 Cyclohexanone 16.1 Butoxyethanol 9.43 Diacetonealcohol 18.2 1-pentanol 16.9 1,2-pentanediol 17.3 Glycerol 46.5

Anionic Dyes Forming a Complex with Fixer

Non-limiting examples of anionic dyes that are effective with thisinvention are: direct black dyes, such as Direct Black 168 (DB168),Direct Black 19 (DB19) or variants of Fast Black 2; phthalocyanine cyandyes, such as ProJet Cyan 485; acid cyan dyes, such as Acid Blue 9(AB9); mixtures of acid cyan and phthalocyanine cyan, such as AB9 andProJet Cyan 485 (PJ485); gamma acid magenta dyes, such as Magenta 377(M377); H-acid magenta dyes, such as ProJet Magenta 364 (M364); Xanthenemagenta dyes, such as Acid Red 289 (AR289); mixtures of H-acid magentaand Xanthene magenta dyes, such as mixtures of ProJet Magenta 364 andAR289; direct yellow dyes, such as Direct Yellow 132 (DY132); acidyellow dyes such as Acid Yellow 23 (AY23); and mixtures of direct yellowdyes and acid yellow dyes, such as mixtures of DY132 and AY23.

Cationic Polymeric Fixers Forming a Complex with Anionic Dyes

In a preferred embodiment of the fixer, polyguanidines andpolyethyleneimines, have been found to be effective cationic polymersfor this purpose.

In a more preferred embodiment, the cationic polymers arepolymonoguanidines, preferably poly (C₃₋₁₈-hydrocarbyl monoguanidines).

In a most preferred embodiment, the poly(C₃₋₁₈-hydrocarbylmonoguanidines) comprise groups selected from the group consisting ofFormula (1) and Formula (2) or salts thereof:

wherein:

each m is independently 0 or 1;

each Y is independently a C₂₋₁₈-hydrocarbyl group;

A and B are hydrocarbyl groups which together comprise a total of 3 to18 carbon atoms; and

each R is independently hydrogen, alkyl, alkoxy, substituted alkyl orsubstituted alkoxy.

In another most preferred embodiment, the poly(C₃₋₁₈-hydrocarbylmonoguanidines) comprise at least one group of Formula (3) or saltsthereof:

wherein:

n is from 2 to 50.

EXAMPLES Example 1

For each of Runs 1, 2 and 3, 1 microliter anionic dye-based ink andcationic polymeric fixer is pipetted in the order Fixer/Color/Fixer foreach of colors black, cyan, magenta and yellow onto cellulose thin layerchromatography (TLC) plates. The three TLC plates were dried for 30minutes at ambient temperature. The TLC plates were developed in solventat 55° C.

The table below summarizes the mobility of Run 1, Run 2, and Run 3dye/fixer complex/precipitates in various water-based servicingsolvents.

TABLE 1 Run/ Dipropylene 1,2 Tetraethylene Diethylene Ink Dye Fixerglycol Hexanediol Water glycol glycol 2-pyrrolidone Run Direct BlackPoly-alkyl Immobile Immobile Immobile Slight Slight Moderate 1/K amineRun Phthalocyanine Poly-alkyl Immobile Immobile Immobile ImmobileImmobile Slight 1/C cyan amine Run Gamma acid Poly-alkyl ImmobileImmobile Immobile Immobile Immobile Completely 1/M magenta amine RunDirect yellow Poly-alkyl Immobile Immobile Immobile Slight ModerateCompletely 1/Y amine Run Direct Black Poly-guanidine Immobile ImmobileImmobile Slight Slight Moderate 2/K (different from 1/K) RunPhthalocyanine Poly-guanidine Immobile Immobile Immobile ImmobileImmobile Slight 2/C cyan Run H-acid Poly-guanidine Immobile ImmobileVery Slight Moderate Moderate 2/M magenta slight Run Direct yellowPoly-guanidine Immobile Immobile Immobile Slight Moderate Completely 2/YRun Direct Black Poly-guanidine Immobile Immobile Immobile Slight SlightModerate 3/K (different from 1/K) Run Mixture of acid Poly-guanidineImmobile Immobile Immobile Slight Slight Moderate 3/C cyan andphthalocyanine cyan Run Mixture of H- Poly-guanidine Very slight Veryslight Very Slight Moderate Moderate 3/M acid magenta slight andxanthene magenta Run Mixture of Poly-guanidine Immobile Immobile VerySlight Moderate Completely 3/Y direct yellow slight and acid yellow

Example 2

For each of Runs 4, 5 and 6, 1 microliter anionic dye-based ink andcationic polymeric fixer is pipetted in the order Fixer/Color/Fixer foreach of colors black, cyan, magenta and yellow onto cellulose TLCplates. The three TLC plates were dried for 30 minutes at ambienttemperature. The TLC plates were developed in various water-basedservicing solvent at 55° C.

The table below summarizes the mobility of Run 3, Run 4, and Run 5dye/fixer complex/precipitates in the various solvents.

TABLE 2 2-amino-2- methyl Fixer/ Butoxy- Diacetone propanol 1,2- Ink DyeFixer Cyclohexanone ethanol alcohol (AMP) propanediol Run DirectPolyalkyl Immobile Immobile Immobile Moderate Slight 4/K Black amine RunPhthalocyanine Polyalkyl Immobile Immobile Immobile Completely Immobile4/C cyan amine Run Gamma Polyalkyl Immobile Immobile Immobile ModerateVery 4/M acid amine slight magenta Run Direct Polyalkyl ImmobileImmobile Immobile Completely Slight 4/Y yellow amine Run Direct Poly-Immobile Immobile Immobile Immobile Slight 5/K Black guanidine(different from 1/K) Run Phthalocyanine Poly- Immobile Immobile ImmobileImmobile Very 5/C cyan guanidine slight Run H-acid Poly- ImmobileImmobile Immobile Immobile Moderate 5/M magenta guanidine Run DirectPoly- Immobile Immobile Immobile Slight Moderate 5/Y yellow guanidineRun Direct Poly- Immobile Immobile Immobile Slight Slight 6/K Blackguanidine (different from 1/K) Run Mixture Poly- Immobile ImmobileImmobile Slight Moderate 6/C of acid guanidine cyan and phthalocyaninecyan Run Mixture Poly- Very Very Very slight Slight Moderate 6/M ofH-acid guanidine slight slight magenta and xanthene magenta Run MixturePoly- Immobile Immobile Immobile Slight Moderate 6/Y of direct guanidineyellow and acid yellow

Example 3

A stock solution of ink containing anionic dye, Acid Blue 9(AB9), andfixer containing cationic polymer, Polyguanidine, are diluted withratios of water and 2-P. For steady state solubility, equal volumes ofthe ink solutions and the fixer solutions are mixed. Solubility isdetermined by examining the mixture for precipitate after 1-day atambient conditions

Stock solutions are listed in Table 3A below:

TABLE 3A Ink A FIXER B Components % active Components % active Dye AB-96 Polyguanidine 4 Bis(2- 0.90 1,2-Hexanediol 7.5ethylhexyl)sulfosuccinate Fluorocarbon surfactant 0.30 2,3,4,5- 7.5Tetrahydrothiophene- 1,1-dioxide 4-Octylphenol 0.4 Fluorocarbon 0.3Polyethoxylate surfactant Na₂EDTA 0.2 POE (4) lauryl ether 0.4 MOPS 0.4B-Alanine 0.2 Na₂EDTA 0.05

Table 3B below summarizes the solubility of Ink A and the PolyguanidineFixer at various water/2P ratios. The concentration of 2-pyrrolidone hasa strong effect on the interaction of the dye and fixer. Increasing theconcentration of 2-P increases the solubility of the dye/fixer complex.

Weight % Weight % ppt with ppt with Sample (Dye) water Weight % 2PSample X Sample Y 1 0.60 90 0 Yes Yes 2 0.60 80 20 Yes Yes 3 0.60 60 40Yes None 4 0.60 40 60 Yes None 5 0.60 20 80 Yes None 6 0.60 0 90 NoneNone Weight % Weight % Sample (Fixer) water Weight % 2P X 2 98  0 Y 2 4850In >45% 2-P, Ink A/Polyguanidine Fixer complex does not precipitate.

Example 4

The solubility of the DB168 Dye/Polyguanidine Fixer complex was testedin various solvents. Dye and fixer were added to aqueous cosolventsolutions to attain a concentration of 9.4 g/L DB168 Dye and 9.4 g/LPolyguanidine Fixer—the resulting mixture partitions into a liquidsupernatant phase and a solid precipitate phase. Entries in Table 4below represent the % of the total colorant that goes into thesupernatant phase (100% would represent complete dye/fixer solubility ina solvent). The data shows that DB 168 Dye/Polyguanidine Fixer is themost soluble in 88% 2P—and that the reproducibility of this measurementis good (comparing ‘2P’ and replicate ‘2P-2’). It also shows that therelative ability of solvents to dissolve the dye/fixer complex changesas water is taken out of the system. For example, at 44% aq TMS is abetter solvent for DB 168 Dye/Polyguanidine Fixer than 44% aqueous TEG,but 88% aqueous TEG is a better solvent than 88% aqueous TMS.

44% solvent 88% solvent 2-pyrrolidone 0.28 34.27 2-pyrrolidone (rep 2)0.27 34.87 1,2-hexanediol 0.11 0.18 Tetramethylene sulfone 0.38 7.631-methyl-2-pyrrolidone 0.45 30.54 1,2-propanediol 0.00 0.67 Diethyleneglycol 0.00 3.47 Tetraethylene glycol 0.00 8.86 Glycerol 0.00 0.00Ethylene glycol 0.00 0.40 Tetrahydrofuran 1.32 15.45n,n-dimethylpropionamide 0.76 20.30

Example 5

Fixer-dye mixtures containing 0, 8, and 40% 2P were made by mixing 3% ofdye in water or in 40% 2P with 3% of FA11/5 (polymonoguanidine) or FA2(polybiguanadine) in water, pH adjusted to 4. Higher 2P-containingsolutions (40% 2P in mixture) were prepared by mixing 3% dye in waterwith 6% FA11/5 or FA2 (in water, pH adjusted to 4) As dyes, PJ485, AB9,M364, AR289, DY132, AY23-TMA, DB19 and DB168 were used in this study.The samples were centrifuged.

The “Colorant Soluble” was plotted in FIGS. 1, 2, 3 in DI water, 8% 2Pand 40% 2P, respectively, where “% Colorant Soluble” is defined asabsorbance at λ_(max) (w/o fixer). For DB168 and DB19, the minimum of “%Colorant Soluble” was reached at ˜0.5 fixer/dye ratio. There wasvirtually no difference observed in “% Colorant Soluble” of thefixer-black dye complexes using FA2 or FA11/5.

Regardless of fixer type or % 2P present in the solution, fixer-DB168complex is the least soluble. Fixer-DB19 complex was more soluble thanfixer-DB168 complex but still less soluble than most of the fixer-colordye complexes.

As shown in FIG. 4, “% Colorant Soluble” increased with increasing % 2P.The amount of colorant soluble increased by roughly one order ofmagnitude from 0 to 40% 2P for most dyes including DB19. “% ColorantSoluble” of fixer-DB168 appeared to be insensitive to 2P content in thisregion.

Example 6

As in Example 1, 1 microliter anionic dye-based ink and cationicpolymeric fixer is pipetted in the order Fixer/Color/Fixer for each ofcolors black, cyan, magenta and yellow onto cellulose thin layerchromatography (TLC) plates. The TLC plates were dried for 30 minutes atambient temperature. The TLC plate was developed in solvent at 55° C.

The table below summarizes the mobility of Run 2 dye/fixercomplex/precipitates in various additional water-based servicingsolvents. The dielectric constants at standard temperature and pressureare given for each of the solvents. Both “ineffective” and “effective”solvents are included on the list. The more “effective” solvents tend tooccur within the range of 20-41 dielectric constant at standardtemperature and pressure.

TABLE 6 Run/ 1,2- Triethylene 1,5- 1,4- Ethylene Ink Dye Fixer1-pentanol pentanediol glycol pentanediol butanediol glycol Run DirectPoly- Immobile Slight Slight Immobile Very slight Slight 2/K Blackguanidine Run Phthalocyanine Poly- Immobile Very slight Slight SlightSlight Moderate 2/C cyan guanidine Run H-acid Poly- Immobile Very slightSlight Slight Slight Moderate 2/M magenta guanidine Run Direct Poly-Immobile Immobile Slight Very slight Slight Moderate 2/Y yellowguanidine Dielectric Constants at STP 16.9 17.3 23.7 26.2 31.9 41.4

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

1. An inkjet printhead cleaning system, comprising: an inkjet printerconfigured to print inks including anionic dyes and fixers includingcationic polymers respectively as separate fluids such that complexes ofanionic dyes and cationic polymers accumulate on a printhead of theprinter and other surfaces of the printer as printing is conducted; anda water-soluble solvent and water mixture configured to be applied tothe complexes accumulated on the surfaces throughout the printer, thesolvent having a dielectric constant from 20 to 43 at standardtemperature and pressure; wherein the anionic dyes in the complex areselected from the group consisting of direct black dyes, phthalocyaninecyan dyes, acid cyan dyes, mixtures of acid cyan and phthalocyaninecyan, gamma acid magenta dyes, xanthene magenta dyes, mixtures of H-acidmagenta and xanthene magenta dyes, direct yellow dyes, acid yellow dyes,and mixtures of direct yellow dyes and acid yellow dyes; wherein thecationic polymers are selected from the group consisting ofpolyalkylamines, polyethyleneimines and polyguanadines; and wherein thewater-soluble solvent and water mixture is one of the following: atleast 44 weight % of the water-soluble solvent, the water-solublesolvent selected from the group consisting of 1-methyl-2-pyrrolidone andn,n-dimethylpropionamide; at least 88 weight % of the water-solublesolvent, the water-soluble solvent selected from the group consisting ofdiethylene glycol, 1,2-propanediol, and tetraethylene glycol; or atleast 40 weight % 2-pyrrolidone included in the solvent and watermixture.
 2. The inkjet printhead cleaning system of claim 1, wherein theweight percent ratio of 2-pyrrolidone to water is 40:60.
 3. The inkjetprinthead cleaning system of claim 1 wherein the cationic polymers arepolymonoguanadines.
 4. The inkjet printhead cleaning system of claim 3wherein the polymonoguanadines are poly(C₃₋₁₈-hydrocarbylmonoguanidines).
 5. The inkjet printhead cleaning system of claim 4wherein the poly(C₃₋₁₈-hydrocarbyl monoguanidine) comprises groupsselected from the group consisting of Formula (1) and Formula (2) orsalts thereof:

wherein: each m is independently 0 or 1; each Y is independently aC₂₋₁₈-hydrocarbyl group; A and B are hydrocarbyl groups which togethercomprise a total of 3 to 18 carbon atoms; and each R is independentlyhydrogen, alkyl, alkoxy, substituted alkyl or substituted alkoxy.
 6. Theinkjet printhead cleaning system of claim 4 wherein thepoly(C₃₋₁₈-hydrocarbyl monoguanidine) comprises at least one group ofFormula (3) or salts thereof:

wherein: n is from 2 to
 50. 7. A method of removing an anionicdye/cationic polymer complex from an inkjet printhead and other surfacesof the printer as printing is conducted, comprising the step of applyingto the complex on the printhead and other surfaces of the printer awater-soluble solvent and water mixture, the solvent having a dielectricconstant from 20 to 43 at standard temperature and pressure; wherein theanionic dyes in the complex are selected from the group consisting ofdirect black dyes, phthalocyanine cyan dyes, acid cyan dyes, mixtures ofacid cyan and phthalocyanine cyan, gamma acid magenta dyes, xanthenemagenta dyes, mixtures of H-acid magenta and xanthene magenta dyes,direct yellow dyes, acid yellow dyes, and mixtures of direct yellow dyesand acid yellow dyes; wherein the cationic polymers are selected fromthe group consisting of polyalkylamines, polyethyleneimines andpolyguanadines; and wherein the water-soluble solvent and water mixtureis one of the following: at least 44 weight % of the water-solublesolvent, the water-soluble solvent selected from the group consisting of1-methyl-2-pyrrolidone and n,n-dimethylpropionamide; at least 88 weight% of the water-soluble solvent, the water-soluble solvent selected fromthe group consisting of diethylene glycol, 1,2-propanediol, andtetraethylene glycol; or at least 40 weight % 2-pyrrolidone included inthe solvent and water mixture.
 8. The method of claim 7, wherein theweight percent of 2-pyrrolidone to water 40:60.
 9. The method of claim 7wherein the cationic polymers are polymonoguanadines.
 10. The method ofclaim 9 wherein the polymonoguanadines are poly (C₃₋₁₈-hydrocarbylmonoguanidines).
 11. The method of claim 10 wherein thepoly(C₃₋₁₈-hydrocarbyl monoguanidine) comprises groups selected from thegroup consisting of Formula (1) and Formula (2) or salts thereof: t,0050wherein: each m is independently 0 or 1; each Y is independently aC₂₋₁₈-hydrocarbyl group; A and B are hydrocarbyl groups which togethercomprise a total of 3 to 18 carbon atoms; and each R is independentlyhydrogen, alkyl, alkoxy, substituted alkyl or substituted alkoxy. 12.The method of claim 10 wherein the poly(C₃₋₁₈-hydrocarbyl monoguanidine)comprises at least one group of Formula (3) or salts thereof:

wherein: n is from 2to
 50. 13. A method of using a water-soluble solventand water mixture, the solvent having a dielectric constant from 20 to43 at standard temperature and pressure to remove an anionicdye/cationic polymer complex from an inkjet printhead and other surfacesof the printer as printing is conducted, comprising the step of applyingthe complex onto the printhead; wherein the anionic dye in the complexis selected from the group consisting of direct black dyes,phthalocyanine cyan dyes, acid cyan dyes, mixtures of acid cyan andphthalocyanine cyan, gamma acid maaenta dyes, xanthene magenta dyes,mixtures of H-acid magenta and xanthene magenta dyes, direct yellowdyes, acid yellow dyes, and mixtures of direct yellow dyes and acidyellow dyes; wherein the cationic polymer is selected from the groupconsisting of polyalkylamines, polyethyleneimines and polyguanadines;and wherein the water-soluble solvent and water mixture is one of thefollowing: at least 44 weight % of the water-soluble solvent, thewater-soluble solvent selected from the group consisting of1-methvl-2-pyrrolidone and n,n-dimethylpropionamide; at least 88 weight% of the water-soluble solvent, the water-soluble solvent selected fromthe group consisting of diethylene glycol, 1,2-propanediol, andtetraethylene glycol, or at least 40 weight % 2-pyrrolidone included inthe solvent and water mixture.
 14. The method of claim 13, wherein theweight percent ratio of 2-pyrrolidone to water 40:60.
 15. The method ofclaim 13 wherein the cationic polymers are polymonoguanadines.
 16. Themethod of claim 15 wherein the polymonoguanadines are poly(C₃₋₁₈-hydrocarbyl monoguanidines).
 17. The method of claim 16 whereinthe poly(C₃₋₁₈-hydrocarbyl monoguanidine) comprises groups selected fromthe group consisting of Formula (1) and Formula (2) or salts thereof:

wherein: each m is independently 0 or 1; each Y is independently aC₂₋₁₈-hydrocarbyl group; A and B are hydrocarbyl groups which togethercomprise a total of 3 to 18 carbon atoms; and each R is independentlyhydrogen, alkyl, alkoxy, substituted alkyl or substituted alkoxy. 18.The method of claim 16 wherein the poly(C₃₋₁₈-hydrocarbyl monoguanidine)comprises at least one group of Formula (3) or salts thereof:

wherein: n is from 2to 50.